Siemens SINAMICS G130 Engineering Manual page 71

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If it is acceptable to operate the DC link at half power if an Active Infeed fails, each Active Infeed can be
dimensioned for half the infeed current, taking into account a current derating of 5% with respect to the rated
current. If the full infeed power is required if an Active Infeed fails, each of the two Active Infeeds and the
associated transformer windings must be dimensioned for the full power required for the DC link.
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Each Active Line Module in conjunction with its Active Interface Module must be able to precharge the
complete common DC link capacitance.
Variant 3 with Active Infeed (master-slave configuration); boundary conditions to be observed:
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The Active Infeeds (master and slave(s)) must be electrically isolated on the line side to prevent circulating
currents that may otherwise occur between the systems as a result of autonomous, unsynchronized
operation with independent Control Units.
Depending on whether the Active Infeeds are supplied from a common low-voltage supply system or from
different medium-voltage supply systems, a distinction is made between two configurations:
a) Supply from a common low-voltage supply system:
- The master infeed is connected directly to the low-voltage supply system, whereby the supply system can
be operated as either a grounded (TN) or non-grounded (IT) supply system. With respect to voltage loads
on the DC link and on the motor windings to ground, however, operation with a non-grounded IT supply
system is preferable.
- The slave infeed(s) must be supplied by its / their own isolation transformer, whereby all secondary
windings must be non-grounded.
Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual - May 2008
© Siemens AG
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